The main components of a drive-train are a drive aggregate and a transmission, the transmission being connected between the drive aggregate and a drive output of the drive-train. The transmission converts rotational speeds and torques and thereby transmits the traction force supplied by the drive aggregate and provides it at the output of the drive-train. The present invention concerns a method for operating a drive-train which, besides the drive aggregate, transmission and output already mentioned, also comprises a starting clutch connected between the drive aggregate and the transmission. The transmission of the drive-train is preferably in the form of an automatic or semi-automatic transmission, in particular an automatic or semi-automatic manual transmission.
From practice it is already known to operate a drive-train for rolling and coasting during thrust operation, in such manner that a target value for the position of the starting clutch connected between the drive aggregate and the transmission is determined as a function of a transmission input speed, then comparing the target value for the position of the starting clutch with a corresponding actual value, so that in a regulator, on the basis of the deviation between the target and the actual values, an adjustment parameter for adjusting the starting clutch is generated, namely in such manner that by virtue of the adjustment of the starting clutch, the actual value approaches the target value. Thrust operation of the drive-train is understood to mean movement, i.e. in this case rolling or coasting, during which an accelerator pedal or gas pedal of the drive-train is not actuated, or whose actuation is smaller than a specified limit value. During rolling or coasting a gear is engaged in the transmission.
In methods known from practice for operating a drive-train in the thrust mode during rolling or coasting, the target value for the position of the starting clutch is preferably determined from a characteristic curve, the same curve being used for rolling and for coasting, so that for a defined value of the transmission input speed in each case the same target value for the position of the starting clutch is determined both for rolling and for coasting. Owing to inertial effects in the control system of the starting clutch, in this case, for example when rolling downhill, the transmission input speed may exceed the speed of the drive aggregate until the starting clutch, which has to be closed farther, has accelerated the drive aggregate to the level of the transmission input speed. Because of this the drive-train becomes somewhat slower, so with decreasing transmission input speed the starting clutch can be opened more easily, in order to be closed again subsequently. In a drive-train prone to oscillations this can lead to resonance effects of the drive-train, since the transmission input speed influences the target value for the position of the starting clutch and is thus regeneratively coupled to the target value for the position of the starting clutch. Such upswings of a drive-train with oscillating movement of the starting clutch impairs the driving comfort and is therefore disadvantageous.
As already mentioned, in the methods known from practice the control parameter for adjusting the starting clutch is determined as a function of the deviation between the target value for the position of the starting clutch and the corresponding actual value, the control parameter typically being an adjustment speed for the starting clutch in its closing or opening direction. This too can result in uncomfortable driving behavior.
As prior art, the documents DE 103 34 930 A1 and DE 10 2007 012 875 A1 can be mentioned, each of which discloses a method for operating a drive-train in the thrust mode.